Electrical socket having a movable shutter to cover its contact openings



April 3, 1956 s. G. YOUNG 4 ELECTRICAL SOCKET HAVING A MOVABLE SHUTTER TO -COVER ITS- CONTACT OPENINGS Filed Jam. 26, 1954 3 Sheets-Sheet l JUHHHHH Aprll 3, 1956 s. G. YOUNG 4 ELECTRICAL SOCKET HAVING A MOVABLE SHUTTER TO COVER ITS CONTACT OPENINGS Filed Jan. 26, 1954 3 Sheets-Sheet 2 April 3, 1956 s. G. YOUNG 2,740,943

ELECTRICAL SOCKET HAVING A MOVABLE SHUTTER TO COVER ITS CONTACT OPENINGS Filed Jan. 26, 1954 3Sheets-Sheet 5 United States Patent ELECTRICAL SOCKET HAVING A MOVABLE IJgTER TO COVER ITS CONTACT OPEN- Sidney Geoffrey Young, London, England Application January 26, 1954, Serial No. 406,153 11 Claims. (Cl. 339-40) This invention relates to shutters for electrical socket outlets, more particularly outlets of the type used in conjuction with 3-pin plugs. The pins may be of the round or flat type, or any other section that may from time to time be employed in electric plugs. Such shutters are movable on insertion of the plug pins, thus exposing the sockets and making it possible for electrical contact to take place between the pins of the plug and such sockets.

The principal objects of the invention include provision of one or more of the following features:

(a) A shuttered socket outlet in which the live sockets are normally screened by an insulating shutter and the shutter can only be fully released from its screening position by the insertion of all three pins.

(15) Insertion of the earth pin'alone or an object capable of entering the earth socket does not expose the live sockets which remain still screened by the shutter.

(c). A pin or similarly shaped object cannot alone unscreen alive socket.

((1) Even after insertion of the earth pin into the earth socket, any subsequent pressure. exerted upon. only one of the parts of the shutter obscuring the live sockets does not cause exposure of either live socket.

(e) The shutter is located between two close horizontal planes extending parallel to the surface of thesocket outlet cover, and is capable of incorporation within such cover.

(1) A generally simplified construction, with particular reference to ease of manufacture and assembly, and employment of only a simple leaf spring.

The basic principle of the invention is illustrated in Figure 1 of the annexed drawings, which figure shows, on a much enlarged scale, a purely diagrammatic, representation of a shutter member and the surfaces of a housing in its immediate vicinity. 1

Figure 2 shows a rear elevation view of a socket outlet and shutter assembly according to the invention (as seen from the right in Fig. 3);

Figure 3 shows a section on the line IIIIII in Fig. 2; and 1 Figure 4 shows a fragmentary section on the line IV-IV of Fig. 3.

In these three latter figures the shutter parts are shown in their neutral position obscuring the live sockets. In addition to the drawings include:

Figure 5, which is a view similar to Fig. 4 with the parts in the partially open position;

Figure 6, which is a further similar view with the parts in the fully open position;

Figure 7, which is a view similar to Figs. 4 to 6 but with the parts in one locked position; and

Figure 3, which is a view similar to Figures 4 to 6' but with the parts in a second locked position.

Figure 9 shows the general arrangement of a shutter 41 having hooks 42 and 43 arranged externally at both ends of the shutter respectively;

Figure 10 shows the general arrangement of a shutter 44 having hooks 45 arranged externally at the lower end of the shutter and hooks 46 arranged internally at the upper end; and

Figure 11 shows the general arrangement of a shutter 47 having hooks 48 and 49 arranged internally at both ends of the shutter respectively.

This shutter member, designated by the numeral 1, is shown in said Figure 1 in its normal neutral position. It is of approximately inverted T shape with a forked stem, having angular upper limbs ql, q2, a slot S, a curved base C and three cam surfaces F1, F2 and F3 inclined to the plane of the member. The numeral 2 designates a flat leaf spring which causes the movable member 1 to occupy the position shown; and 3 is a cavity in the cover of the socket outlet having an outline as shown, which acts to guide the movable member 1 into its various positions and also to provide tangential support for the leaf spring 2.

The action of the shutter is as follows:

On insertion of the plug earth pin (not shown), which is longer than the live pins, the rounded end of the pin makes contact with cam surface Fa via the opening 03 in the cover plate. This insertion moves the shutter member 1 so that the upper edge N of the cam surface F3 takes up a position on the line L1-L1. At the same time points Q1 and Q2 of the limbs ql, q2 are moved vertically to take positions (shown in dotted lines) adjacent corners P1 and Pr. moulded into the housing. The cam surfaces F1 and F2 arethen exposed through apertures 01 and O2 in the cover plate, the slot S in the member 1 having moved with respect to a guide pin W provided on the housing and extending with some slight clearance into the slot S. The leaf spring 2 is urged downwards and its points of sup-' port T1 and T2 move down inclines H1 and m.

Further pressure exerted on the plug (as a whole) will cause the live pins to engage the cam surfaces F1 and F2 through the openings 01 and 02 causing the shutter member 1 to travel further downwardly. During this normal travel the points Q1 and Q2 will pass between the corners P1 and P2 so that the live pins can readily enter the sockets arranged beyond theshutter. It will be noted 7 that the fiat spring 2 will have been deflected further,

but as both its ends are free the points of support of the ends will have moved further down the inclines H1 and E.

On releasing the shutter member by'withdrawal of the plug, it will move vertically upwards and assume its original position screening the live sockets.

As already explained, insertion of the earth pin into the aperture 03 causes the edge N to be in line with L1-L1. At this level the points Q1 and Q2 of the screen 1 are in close proximity to the projecting corners P1 and P2 and the cam faces F1 and F2 are exposed through the apertures 01 and 02. Should then any suitably shaped object be passed through either one of the apertures 01 or 02 to press on the respective cam face, the screen will become locked by engagement between either P1 and Q1 or P2 and Q2, since any pressure exerted on either one of the cam surfaces F1 or F2 alone, will cause the member 1 to rotate as a whole approximately about the pin W, the curved edge of the screen C rolling on the spring 2. Suflicient clearance K between the parallel sides of the member 1 and the cavity 3 is provided to enable this ro- 3 ceding and associated with the rotational movement does not expose or even partially expose a live socket.

Consideration of the rotational movement shows that the pin W or the point of contact of the screen with the spring or a point slightly below such point of contact will provide the axis of rotation, and the dimensions are such as to give maximum magnification to the movement of the screen limbs and (11 and as relative to the angular movement of either of the cam surfaces without interfering with normal insertion of the three plug pins.

The inclined surfaces H1 and A2 are so arranged that large deflection of the leaf spring 2 can take place without appreciable shortening of the working length of the spring, this being achieved by arranging the angle of inclination of the surfaces H1 and H2 approximately tangential to the ends T1 and Tz of the leaf spring in the fully stressed position. This arrangement at the same time allows the spring to regain its original position on removal of the plug from the socket outlet and greatly simplifies manufacturing and design considerations by permitting the use of a leaf spring. The spring may be pro-stressed in the neutral position, if desired.

The above described construction of the shutter can be modified in several ways without substantially departing from the basic operational features. For instance, locking of the screen in the cavity can be effected on any surfaces of the edges of the shutter. It could alternatively be carried out at the slot by an extension at right angles, the locking means being the pin W.

According to another modification, the movable shutter may be made in two parts, abutting against each other, the first part being the cam surface obscuring the earth socket and its downward extension, whilst the second part is the remainder of the movable member. The first part maybe provided with a slot or similar arrangement so that its downward travel can be limited by a pin projecting into the slot. The limit of this downward travel is reached when the earth pin has been inserted into the opening 03 and the edge N reaches the line L1-L1. The remaining part of the movable member is then caused to travel its full length independently by engagement of the live pins with the then exposed cam surfaces therefor. The first part may take the form of a loose metal insert appropriately provided with a cam surface, since this part of the shutter does not normally become alive.

A practical development of this latter proposal incorporated in a shutter mechanism employing the general principles already explained with reference to Figure l, is illustrated in Figures 2 to 8 of the annexed drawings, in which the socket outlet assembly 10 is mounted on the rear of a fiat housing 11 containing the main shutter 12 (also in the form of a flat plate and moulded to the shape shown in Figs. 4-8 from a suitable insulating material) and a separate metal member 13 which forms part of the shutter mechanism. These parts are held within the housing 11 by a back plate 14 itself secured to the housing 11 by screws 15 and a strap 16 that also serves to position the outlet assembly 10. This assembly, the details of which are of no relevance to the present invention, consists of an earth socket 17 connected electrically to the strap 16 and an earth terminal 13, and two live sockets arranged on each side of the interior of the assembly. These live sockets are not themselves visible in any of the figures, although their terminals 12 and holes 20 providing screw-driver access to the sockets are shown in Figure 2. Suffice it to say that the particular construction here illustrated is adapted for the reception of a plug having pins of rectangular section (the construction reviously described with reference to Fig. 1 being, of course, primarily designed to receive pins of round section), and that the housing 11 is provided with suitable apertures for the passage of these pins. An aperture 21 for the'carth pin is visible in Figs. 3-7, and the relative position of the apertures for the live pins is indicated by the broken lines 22 in Figs. 4 and 8.

The shapein plan view of the interior of the housing 11 is best seen from Figs. 4-8. In addition it has two parts projecting into its interior, the first being a guideway 23 for the metal member 13, which includes a small bridge 24 (Fig. 3) for limiting movement of such member 13, and the second being a post 25 that co-operates with a slot 26 in the main shutter 12.

This shutter 12 is of generally the same shape as the member 1 described earlier, except that the division of its stem into two limbs is more pronounced. These limbs, 27 and 23 in the embodiment now being described, are provided with hooks 29 and 30 adapted to co-operate with shoulders 31 and 32 formed in the housing 11 in a similar manner to that already described. In addition to these engaging surfaces, the slot 26 is also provided with a pair of shoulders 33, the post 25 having a fiat upper surface capable of establishing a locking engagement with either of these shoulders 33. A cam surface 34 is provided on the metal member 13, and cam'surfaces 35 and 36 are arranged at the sides of the shutter 12. In the neutral position shown in Fig. 4 the cam surfaces 35 and 36 are not'accessible through the apertures 22.

Considering firstly the normal introduction of a three pin plug into the device, the initial movement results in the earthing pin 37 bearing against the cam surface 34 of the member 13, whereby this member and with it the shutter 12 is slid downwardly to the position shown in Fig. 5, against the pressure of a leaf spring 38, the ends of this spring 38 sliding down inclined surfaces 50. The cam surfaces 35 and 36 are then in register with the apertures 22, so that continued insertion of the plug causes pressure to be exerted on these surfaces by the live pins 39 thereof, and the shutter 12 to be moved further downwardly to the position shown in Fig. 6. The metal member 13 follows this movement until stopped by abutment of a shoulder 40 thereon against the bridge 24. When thus moved to its fully open position the shutter allows free access to the live sockets for the live pins 39.

As in the basic construction described with reference to Fig. 1, unequal pressures on the two cam surfaces 35 and 36 prior to this final part of the opening movement, e. g. a greater pressure on the cam surface 35, causes the shutter 12 to pivot from the Fig. 5 position to a locking position, shown in Fig. 7, in which the hook 29 engages the shoulder 31. Further downward sliding movement of the shutter 12 is thus prevented and the live sockets remain obscured. Removal of the earthing pin 37 or Whatever objects has been inserted through the aperture 21 in lieu thereof, will be necessary to permit the shutter to be returned to its neutral position and there to be reoriented centrally by reason of the close fit of'the top ends of the limbs 27 and 28 in the housing 11 in this position.

It will be evident that there can be wide variation in the positioning of the engaging hookand shoulderlike surfaces in relation to the positions of the cam surfaces 35 and 36 and the point about which the shutter pivots when unequal pressures are applied to such cam surfaces. As already explained, normally the tendency will be for the shutter to pivot or roll about its lower central surface in contact with the spring 38 (for which reason such surface is curved), in which case the major sideways movement will take place at the upper end of the shutter, i. e. the book 29 or 30 being instrumental in locking of the shutter. Should, however, the downward pressure on the cam surface 35 for example, be combined with an inward lateral pressure on such surface, i. e. tending to urge the whole shutter 12 bodily to the right as viewed in Fig. 5 in addition to imparting a slight anti-clockwise rotation to such shutter, then the hooks 29 and 30 may both be prevented from engaging a respective shoulder 31 or 32. It is primarily to guard against manipulation of the shutter in this way that'the second set of interlocking surfaces isprovided, lye. the post 25 and shoultation is shown in Fig. 8, tie right hand shoulder 33 engaging the upper surface of the post 25 to lock the shutter in a second locking position. In some instances, of course, both sets of locking surfaces may engage simultaneously as when the shutter 12 is moved sideways without being rotated.

These considerations may be summarised by the statement that it is desirable, although not necessarily essential, to provide locking surfaces both comparatively near the cam surfaces presented in the live pins of the plug (to cater for sideways sliding of that part of the shutter), and at points comparatively remote from the point about which the shutter tends to pivot when a force is applied to one such cam surface. Since it will normally be preferred to arrange these cam surfaces comparatively near such pivoting point, it follows that the locking surfaces arranged remote from said point will also normally be remote from the cam surfaces. It is largely considerations of this character that have lead to designing of the shutter in the manner shown in Figs. 4 to 8, and in particular the arrangement of hooks 29 and 30 on upwardly projecting limbs (27 and 28) in order to obtain as great a magnification as possible of the lateral movement resulting from a slight rotation of the shutter.

However, either of the sets of locking surfaces may be external to the shutter (as in the case of hooks 29 and 30), or internal to the shutter (as in the case of shoulders 33). Possible variants in this respect are illustrated diagrammatically in Figs. 9 to 11 of the annexed drawings, in which correspondingly positioned shoulders to co-operate with the hooks 42, 43; 45, 46; and 48, 49 will, of course, be provided in the housings and other parts not illustrated indetail will be provided corresponding to the other parts of the shutter 12 already described.

It will be obvious that the movement of the shutter could be upwards instead of downwards with suitable repositioning of the leaf spring, although the arrangement shown is preferred. A still further modification envisaged would be to provide 'a two-directional movement, i. e. a movement of the shutter to one side caused by insertion of the earthing pin, and a subsequent movemovement downwards resulting from insertion of the live pins. An additional spring would be utilised in this case.

In application Where only two plug pins are used instead of three, the construction will be substantial'y the same as described, except that the earth pin cam will be omitted and the relative position of the shutter and the moulded cavity will be that obtaining when previously the earth cam had been moved by the insertion of such pin, i. e. the Fig. 5 position.

It will be evident that other forms of spring may be employed instead of the leaf spring, e g. one or more coil springs. The resilient action may even be attained by the use of rubber or other similar compressible material.

I claim:

1. A shutter assembly for an electric socket outlet having two live sockets, said assembly comprising a housing, a unitary shutter member normally obscuring such live outlets being slidably movable in said housing in one direction to uncover such outlets and also being movable transversely to said first-mentioned direction, cam surfaces on said shutter member to cooperate with the pins of a plug, a pivotal surface formed on the periphery of said shutter member at one end thereof and substantially centrally disposed with respect to said end, spring means engaging such pivotal surface and urging said shutter member to its normal position obscuring said outlets, locking surfaces on said shutter member at or adjacent the end thereof remote from the end having the pivotal surface, such surfaces extending at 6 right angles to the normal direction of sliding movement of said shutter member, and locking surfaces on the housing cooperating with said locking surfaces on said shutter member to lock the same against sliding movement on transverse movement of the shutter member.

2. A shutter assembly according to claim 1, wherein said locking surfaces provided on the shutter are formed externally thereof as projections from the sides of the shutter member.

3. A shutter assembly according to claim 1, wherein the locking surfaces on said shutter member are formed internally thereof as shoulders extending inwardly from the periphery of a slot formed in the shutter member, and the locking surfaces on the housing are formed on a pin projecting into said slot.

4. A shutter assembly according to claim 1, also comprising a second set of similar complementary locking surfaces upon the shutter member and upon the housing, the second set of such locking surfaces on the shutter being situated adjacent the cam surfaces thereon.

5. A shutter assembly for an electric socket outlet adapted to receive a three pin plug of the type having two live pins and an earthing pin longer than such live pins, said assembly comprising a housing with apertures for each such pin, a spring mounted in said housing, a movable flat shutter member mounted in the housing for sliding movement against the pressure of said spring, said member having two cam surfaces adapted to coact with the two live pins, and a pivotal surface at or adjacent one end thereof, means for sliding such member under pressure of the earthing pin against said pivotal surface on the shutter from a neutral position in which said cam surfaces are obscured to a partially open position in which said cam surfaces are in register with the apertures for the live pins, and at least one set of locking surfaces on the movable member extending transversely to the direction of sliding movement thereof to engage with similar locking surfaces on the housing whereby to lock such member against further opening movement unless such latter movement takes the form consequent upon simultaneous pressure of the live pins on the cam surfaces resulting from continued insertion of the plug, such locking surfaces on the shutter being located at or adjacent the end thereof remote from said pivotal surface thereon.

6. A shutter assembly as claimed in claim 5, wherein the means for sliding the member from the neutral to the partially open position comprise a third cam surface formed integrally with said member and arranged in register with the aperture in the housing for the earthing pinwhen said member is in the neutral position.

7. A shutter assembly as claimed in claim 5, wherein the means for sliding the member from the neutral to the par tially open position comprise a separate secondary movable member having a cam surface arranged in register with the aperture in the housing for the earthing pin when said -members are in the neutral position, such secondary member being adapted to move the main member to the partially open position or insertion of the earthing pin but being independent of subsequent movement of such main member.

8. A shutter assembly as claimed in claim 5, wherein the leading edge of the movable member is convexly curved and the spring in said housing is a leaf spring extending transverse to the direction of sliding movement of such member and abutting against the centre of such leading edge.

9. A shutter assembly a claimed in claim 5, wherein one set of locking surfaces is arranged near the leading edge of the movable member in relation to the direction of movement of such member to the fully open position, and one set of locking surfaces is arranged near the trailing edge.

10. A shutter assembly for an electric socket outlet, comprising a housing, a shutter member movable in a recess in said housing and having a pivotal surface formed on the leading edge thereof, an elongated leaf spring extending across such recess and arranged to bear intermediate'of its ends against said pivotal surface and a pair of inclined surfaces with which the ends of the spring engage and along which they may slide on bowing of the spring.

11. A shutter assembly for an electric socket outlet, comprising a housing, a plate-like shutter member slidable in a recess in said housing and having a pivotal surface formed on the leading edge thereof, an elongated leaf spring extending across such recess substantially transverse to the direction of sliding of the shutter member and bearing intermediate of its ends against said pivotal surface, and a pair ofsurfaces on the housing for supporting the ends of said spring, such surfaces extending in a direction intermediate between said direction of sliding and the direction in which the spring extends.

References Cited in the file of this patent UNITED STATES PATENTS 2,477,803 Huber Aug. 2, 1949 FOREIGN PATENTS 443,794 Great Britain Mar. 6, 1936 653,862 Great Britain May 30, 1951 

